It is well known in the art how to manufacture blue gas, sometimes called water gas, in surface facilities. In the typical case aboveground, coal is prepared by removing the fines, so that the charge to gas producer will be reasonably uniform in lump size, for example, 2 to 4 inch thicknesses. Once the gas producer is charged, the fuel is set afire, followed by alternate cycles of blowing with air and runs with steam. Once the gas producer becomes stabilized the alternating cycles are established in rhythm, a set time period for the blow, for example three minutes, followed by a set time period for the run, for example, five minutes, then the cycles are repeated until the fuel is substantially consumed. Then the ash is disposed of and the gas producer is recharged to repeat the process. In this manner during the run cycle blue gas with a calorific content of about 300 BTU per standard cubic foot is manufactured. In reviewing the steps of the method of the prior art it should be noted that there are numerous costly batch operations on the fuel side beginning with the coal which include grub, convey, size, sort, transport, offload; then at the gas producer site: pickup, sort, charge, blow, run and clean up.
In the combustion of a hydrocarbon such as coal, the combustion process occurs either in an oxidizing environment or a reducing environment or a combination of the two. In the oxidizing environment hydrogen combines with oxygen to form water vapor, carbon combines with oxygen to form carbon dioxide, and any sulfur present will combine with oxygen to form sulfur dioxide. In the reducing environment the hydrogen combines with oxygen to form water vapor, carbon combines with oxygen to form carbon monoxide, carbon dioxide (if present) combines with hot carbon to form carbon monoxide, and sulfur combines with hydrogen to form hydrogen sulfide.
Of the products of combustion the ones that are likely to become injurious to plant and animal life are the sulfur compounds. Hydrogen sulfide is a noxious poison which is easily contained in a closed system and can be removed from the exit gases and converted into elemental sulfur by a number of commercial processes. Sulfur dioxide is not so easily separated although there are many noncommercial methods for extracting it from the products of combustion. In reviewing the methods of manufacture of sulfuric acid, a common first step is to convert elemental sulfur into sulfur dioxide in essentially pure form. The sulfur dioxide content of the products of combustion when burning coal, while often in sufficient strength to cause environmental problems, is quite weak in comparison to the strength required for processing into sulfuric acid by processes heretofore known.